A) Field of the Invention
The present invention relates to a communication apparatus equipped with a high-speed data transfer interface and to a digital network system including the communication apparatus.
B) Description of the Related Art
IEEE 1394 Standard published by the Institute of Electrical and Electronics Engineers is known as a serial bus interface standard which can execute a voluminous and rapid digital data transmission. The IEEE 1394 is a high-speed serial interface which has a transmission speed of 100 Mbps, 200 Mbps and 400 Mbps and can transmit a plurality of compressed (encoded) motion picture files such as a MPEG-2 and the like at the same time or an uncompressed (unencoded) motion picture file. Each apparatus that equips with the interface (hereafter called IEEE 1394 device) compliant with the IEEE 1394 Standard performs as one node in the network system. In the IEEE 1394, an isochronous transmission for real time data transmission and an asynchronous transmission for an asynchronous (non-real time) data transmission are supported. That is, the real time data that is a performance data, such as motion picture, voice sound, or MIDI data and the like, is transmitted by using the isochronous transmission, and a non-real data such as a controlling command and a still picture is transmitted by using the asynchronous transmission.
An example of protocol that is compared to an open system interconnection (OSI) referring model of the IEEE 1394 is shown in FIG. 9. The protocol shown in FIG. 9 is defined as a protocol structure based on the “mLAN” (trade-mark) standard. The mLAN standard is connection management technology relating to a music data digital network for music performance data and audio data, the technology using the IEEE 1394 Standard.
As shown in FIG. 9, a protocol stack of the IEEE 1394 is divided into a lower layer and an upper layer, and the lower layer is constituted of four layers of a physical layer, a link layer, a transaction layer and a serial bus management.
The physical layer is a layer for executing a signal process between a transmitted/received electric signal and the link layer. The physical layer regulates a physical interface such as a connector, a cable and the like, an electric interface such as an encoding/decoding which executes an analogue/digital conversion of a logical signal used in the link layer and a signal level which determines an electric level of a communication signal and executes an arbitration for determination of a communication node, resynchronization of a communication clock, initializing detection of the bus and the like. As in the above, the physical layer regulates the physical interface and the electric interface and is generally made of hardware.
The link layer is a layer for executing a signal process between the physical layer and the transaction layer, and it executes an address assignment, a data check, a packet transmission that performs flame distribution of data and a cycle control. In the link layer, the packet transmission service called sub-action and a packet handler that is a packet transmission/reception service are provided. The link layer is also generally made of hardware as same as the physical layer. Also, in the link layer, services concerning to the asynchronous transmission and the isochronous transmission are provided. In the isochronous transmission, processes of the isochronous data such as an audio signal, a video signal and the like are executed not through the transaction layer.
The transaction layer is a layer for executing a signal process between an upper application and the link layer, and it executes a process concerning to the asynchronous transmission. In the transaction layer, one communication process for designated node and address is executed with transmitting a request packet and receiving a response packet by using the process executed by the link layer. Also, a communication process wherein a request packet is received from other node and a response packet is transmitted to the other node is executed. Moreover, the transaction is a data transmission of a request-response type. There are three transaction types, namely, a read transaction, a write transaction and a lock transaction. The read transaction is a transaction used for reading data from a specific target address space. The write transaction is a transaction used for writing data in a specific target address space. The lock transaction is a transaction used for renewing data in a specific target address space in accordance with reference data.
The bus management is a module for intensively managing resources on the serial bus. The bus management includes management of power supplies, management of a topology map and a speed map, management of isochronous resources, and the like. The bus management includes a configuration ROM, a control and status register (CSR) and the like.
As a constitution of a typical communication layer, the physical layer and the link layer are constituted of hardware, and the transaction layer and the bus management are constituted of firmware.
The upper layer is software for managing the lower layer and the whole node, and is constituted of, for example, the 1394AV protocols (IEC-61883) and mLAN upper layer. The AV protocols define a common isochronous packet (CIP) format for expressing the data contents of an isochronous packet, a connection management protocol (CMP) for managing connections by defining a virtual “plug”, a function control protocol (FCP) for managing other devices connected to the IEEE1394 bus, and the like.
The mLAN upper layer is a protocol layer for transmission of audio/music information in accordance with the IEEE 1394 Standard. The mLAN upper layer is constituted of an audio/music information transmission protocol and a connection management protocol both complied with the 1394AV protocols. The audio/music information transmission protocol is used for adding the format for transmitting audio/music information to the definition of CIP. The connection management protocol is used for performing autonomous connection management of each node by using an intelligent CMP.
Also, an AV device protocol that has a typical IEEE 1394 bus is represented with a protocol shown in FIG. 10.
In this protocol structure, each structure is represented by classifying into the lower layer and the upper layer, and into a control system and a signal system. A control type lower layer is formed of the physical layer described before, the asynchronous transmission function provided on the link layer, a read/write transaction based on the asynchronous transmission provided on the transaction layer by using the function of the link layer and the bus management. Also, a control system upper layer is formed of audio/video control (AV/C) model, and a memory read/write based on the asynchronous transmission and a data exchanging function by an asynchronous stream are realized by a controlling lower and upper layer. Moreover, since the control system upper layer has a complicated function, it is general to be equipped with software executed by a CPU.
On the other hand, the signal system is formed of only the lower layer, and the lower layer is formed of the physical layer as described before, the isochronous transmission function provided on the link layer and the packet handler provided on the link layer. The signal system having this structure is a part dealing with an audio signal and a video signal by the isochronous transmission, and it is general to be equipped with hardware because a rapid transaction is needed.
It is approved implicitly that a device having the IEEE 1394 interface equips, as one independent IEEE 1394 node, with both of the IEEE 1394 bus protocol (the lower layer) and thereon a protocol (the upper layer) such as a device control, the isochronous transmission control and the like. In this case, since the upper layer has more complicated function than the lower layer, it equips with software executed by the CPU, and a manufacture cost rises if all the protocol stacks are used. In this case, for example, a powered speaker that is unnecessary to have a complicated user interface and should be cheap needs to be equipped with all the protocol stacks in order to be equipped with the IEEE1394 interface. Therefore, the manufacture cost rises unwillingly.
The applicant of the present invention suggested a network system adopting an IEEE 1394 bus that can solve the problem of the rise of the manufacturing cost in Japanese Patent Application 2001-220895. An example of the network system structure according to the prior art is shown in FIG. 11.
As shown in FIG. 11, the IEEE 1394 bus constituting the network system connects to a dominated node (a node A) equipped only with a lower layer 101a, a dominated node (a node B) equipped only with a lower layer 101b, a dominating node (a node C) that equips an upper layer 102c managing the lower layer 101c, the dominated node A and B together, and a general node (a node D) equipped with a lower layer 101d and an upper layer 102d. In this case, these nodes are physically connected with each another by a daisy chain connection or a tree connection with IEEE 1394 cables. The lower layers 101a to 101c are equivalent to the lower layer shown in FIG. 10, and the upper layer 102c and 102d are, for example, equivalent to the upper layer shown in FIG. 10.
The dominated nodes (the node A and the node B), the dominating node (the node C) and the general node (the node D) may be one of IEEE 1394 devices such as an electric musical instrument, an audio device, an audio/visual (AV) device, a personal computer an external storage device of various types and the like, each having an IEEE1394 interface. The dominated node 3a has no upper layer that manages the lower layer, but it is provided with only the lower layer. Since the dominated node 3a does not have an upper layer, the dominated nodes (node A and node B) themselves cannot normally communicate with the general node (node D) by using a protocol defined by the upper layer. That is, the dominated nodes (node A and node B) having no upper layer cannot process, by themselves, a command based on the 1394AV protocol and a command based on the mLAN standard of which commands are processed by the upper layer.
Since various transactions, the isochronous transmission and the like are processed by the lower layer, the dominated nodes (node A and node B) can process them by themselves. For example, if the dominated node A is a powered speaker, voice signals and the like to be reproduced are transmitted through the isochronous transmission so that they can be processed only by the lower layer. However, connection setting of a reception channel, volume control and the like cannot be processed by the dominated nodes (node A and node B) by themselves with only the lower layer, because a command is received by the upper layer and the upper layer writes data in a function register in the lower layer corresponding to the command by analyzing the command. In a system shown in FIG. 11, communication by the protocol defined by the upper layer can be executed in the dominated odes (node A and node B) by transaction of the upper layer 102c in the dominating node (node C) as an upper layer by proxy of the dominated nodes (node A and node B).
That is, the upper layer of the dominating node (node C) is the upper layer A and the upper layer B for managing the lower layer 101a and 101b of the dominated nodes (node A and node B) in addition to the upper layer C for managing own lower layer. The upper layer 102c is used as the proxy of the upper layer of the dominated nodes (node A and node B), and compatibility of an upper protocol of the dominated nodes (node A and node B) can be maintained. As the result, the dominated nodes (node A and node B) can communicate with the general node (node D) by using the protocol defined by the upper layer.
In the network system shown in FIG. 11, if the upper layer in the dominated nodes (node A and node B) is omitted, the system can maintain a compatibility of the upper protocol, and the dominated nodes (node A and node B) are supplied in a low price. Since the upper layer in the dominating node (node C) has the upper layer in the dominated nodes (node A and node B) together, the structure of the upper layer is complicated, and so it causes that the dominating node (node C) becomes a high price.
Also, there are some cases wherein a compatibility of the upper protocol is not necessary to be assured depending on the applications. In this case, there is a problem that a high-price dominating node is provided although the dominating node is not necessary.